There is a requirement, particularly in the field of environmental or occupational health atmosphere monitoring, for the collection of small samples of atmospheric air in a rapid and simple fashion in a device which is sufficiently economical to produce that disposal following a single use can be justified. Ideally, the device should be of sufficient simplicity that the atmospheric air sample can readily be taken by an essentially untrained person, or by an automated mechanical device, and be of sufficient durability that the device, following sample collection, can be shipped, without any special handling requirements, to a laboratory for analysis.
Canadian Pat. No. 898,193, issued Apr. 18, 1972, teaches a resilient metallic disk-like sampling device of bistable configuration having a fluid inlet/outlet, either in the form of a capillary tube or a small diameter aperture, communicating with an internal sample chamber. In one stable configuration, the expanded configuration, the opposed walls of the device are maximally spaced apart to define therebetween a chamber of maximum specified volume. In the other stable configuration, the collapsed configuration, the opposed walls of the device are minimally spaced apart to define therebetween a chamber of minimum specified volume. The device can be transformed from the expanded configuration to the collapsed configuration by appropriately squeezing the walls of the expanded configuration, with concurrent expelling of the contents of the chamber through the fluid inlet/outlet, such that one of the opposed walls collapses inwardly and "snaps" through an over center position to overlie the other wall in substantially abutting relationship. Conversely, the device can also be transformed from the collapsed configuration to the expanded configuration, again by appropriately squeezing the device to cause the collapsed wall to "snap" outwardly back through the over center position, during the course of which a vacuum is created in the expanding chamber which results in the intake of fluid through the fluid inlet/outlet. The device, due to the resiliency of the metallic construction, can be "snapped" between the expanded and collapsed configurations quite a number of times without rupture.
To collect a fluid sample with the device of Canadian Pat. No. 898,193, it is necessary to establish fluid communication between the fluid inlet/outlet of the device, itself in the collapsed configuration, and a fluid source to be sampled, whereupon the device is "snapped" to transform it into the expanded configuration containing the sample fluid which is drawn into the chamber as it expands. Presuming that analysis of the fluid sample is to be performed at a different location, or at a later time, etc., it is then necessary to appropriately seal the device to preserve the integrity of the fluid sample. Sealing, in the case of a capillary tube type of fluid inlet/outlet can be accomplished by crimping of the bore, whereas in the case of a small diameter aperture sealing can be accomplished by means of a drop of solder or, more preferably, by means of an adhesive metal tape.
A significant disadvantage of the device of Canadian Pat. No. 898,193 is that the cost of manufacture is too high to justify one-time use only. While the device is susceptible to re-use, the necessary cleaning/purging between uses does add to the overall cost of use.
A further disadvantage of the device of Canadian Pat. No. 898,193, as presently commercially available, is the necessity of the separate and additional step of sealing the device, by whatever means.